将图片变为黑白色

/// 将图片变为灰色
+ (UIImage *)lm_grayImage:(UIImage *)image {
    //滤镜处理
    //CIPhotoEffectNoir黑白
    //CIPhotoEffectMono单色
    NSString *filterName = @"CIPhotoEffectMono";
    CIFilter *filter = [CIFilter filterWithName:filterName];
    CIImage *inputImage = [[CIImage alloc] initWithImage:image];
    [filter setValue:inputImage forKey:kCIInputImageKey];

    CIContext *con = [[CIContext alloc] initWithOptions:nil];

    CGImageRef cgImage = [con createCGImage:filter.outputImage fromRect:[inputImage extent]];
    UIImage *resultImg = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);
    return resultImg;
}